<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <script src="https://libs.baidu.com/jquery/2.1.4/jquery.min.js"></script>
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        body{
            background: url(/img/1.jpg) no-repeat center top;
        }
        li{
            list-style: none;
        }
         
        .u{
            float: left;
            margin: 0 1px;
            cursor: pointer;
        }

       
        img{
            width: 50px;
            height: 50px;
        }
    </style>
</head>
<body>
       <div>
           <ul id="u">
               <li id="l"><img src="/img/1.jpg" id="i"> </li>
               <li id="l"><img src="/img/2.jpg" id="i"> </li>
               <li id="l"><img src="/img/3.jpg" id="i"> </li>
               <li id="l"><img src="/img/4.jpg" id="i"> </li>
           </ul>
       </div>
    
       <script>
            $(function(){

                $("img").bind("click",function()
                {
                 $("body").css("background","url("+this.src+")")
                })

            })

       </script>

</body>
</html>